Magnetic position sensing is now widely used in tracking the location of a catheter in the heart, both for diagnostic purposes, such as mapping cardiac electrical activity, and therapeutic, such as ablation of arrhythmogenic tissue. This type of position sensing is implemented in the CARTO® system, produced by Biosense Webster Inc. (Diamond Bar, Calif.).
A magnetic position sensing system of this sort is described, for example, in U.S. Pat. No. 6,690,963, whose disclosure is incorporated herein by reference. The system is used for determining the location and orientation of an invasive medical instrument, such as a catheter or endoscope, relative to a reference frame. It comprises a plurality of field generators, which generate known, distinguishable fields, preferably continuous AC magnetic fields, in response to drive signals. A plurality of sensors are situated in the invasive medical instrument proximate the distal end thereof and generate sensor signals in response to the fields. A signal processor has an input for a plurality of signals corresponding to the drive signals and the sensor signals and produces three location coordinates and three orientation coordinates of a point on the invasive medical instrument.
Catheters having multiple, trackable arms are also known in the art. For example, U.S. Pat. No. 7,099,712, whose disclosure is incorporated herein by reference, describes such a catheter for mapping the electrical activity in a heart. The catheter comprises a plurality of spines, each capable of obtaining electrical, mechanical and locational data. Each spine comprises at least one location sensor and at least one electrode, preferably a tip electrode and at least one ring electrode. The spines may be arranged in an expanded arrangement, wherein each spine extends radially outwardly from the catheter body, or in a collapsed arrangement, wherein each spine is disposed generally along the longitudinal axis of the catheter body. In use, at least one electrode from each spine is positioned in contact with heart tissue to map the electrical activity of the heart. The location sensors are used to determine the location of each point where the electrical activity is monitored.